More specifically it concerns an instrument of the type described in WO 02/065919, in which a spiral or helical tissue receiving element is turned in the tissue from which a sample must be taken, after which the tissue around this tissue receiving element is cut with a sharp cannula around the tissue receiving element and is torn off at the distal end of the tissue receiving element, thereby obtaining a tissue sample in the tissue receiving element. However, this known instrument has a number of disadvantages. They are related to the fibres in the various tissues.
The organs in human and animal bodies have fibres of connective tissue. They give structure to the organ, which normally speaking additionally consist of soft, unstructured tissue. These fibres in organs can run in relatively arbitrary directions or can have one or more primary directions.
It has turned out that, when the tissue to be sampled has ‘unifrontal’ fibres that enter the cut tissue via the frontal connection of the sample to the rest of the tissue, thus where the tissue has to tear loose, and similar fibres that make a curve in order to recede in the same direction, also via this frontal connection, the ‘bifrontal’ fibres, it can happen that the force exerted by the known spiral or helical tissue receiving element is not great enough to tear off these fibres.
As a result it may happen that during the biopsy, the intended tissue sample, that is in the tissue receiving element, is not torn loose from the other tissue and isolated as a sample, but instead of this, while the tissue receiving element is withdrawn from the tissue, the intended sample remains attached to the organ and thus slides out of the receiving space.
When unifrontal fibres are present, but even more so with the presence of lateral fibres, which extend partly transverse to the longitudinal direction of the tissue receiving element and thus protrude through the space between the windings of the spiral or helical tissue receiving element, there is also the disadvantage that the sharp cannula partially pushes the fibres along during the cutting movement, instead of cutting through them, and that these fibres accumulate in the very limited space between the tissue receiving element and the cannula, and thereby impede the movement of the cannula or even make it impossible.
This results in the tissue samples not being cut well, if at all.
Certainly when taking samples from relatively hard tissues, the spiral or helical tissue receiving element can also expand due to the forces acting on it, such that the desired movement of the cannula is hampered or rendered impossible.
It is known, for example in U.S. Pat. No. 6,083,237, to narrow the point, thus the distal end, over a short length, i.e. a maximum of one winding of such a spiral, in order to enable easier penetration into the tissue.
This has the disadvantage that this narrowed point, during insertion, damages the tissue that will later serve as a sample, so that taking an undamaged sample of a certain size is difficult.